To meet the requirements of softness and absorbency, high-quality pulp is still used today for the most part with the absorbency of a pulp determined by fiber length and diameter and freeness. Fibers with a low freeness, as well as large fiber diameters, generally produce bulkier and therefore more absorbent paper. Pulp obtained from conifers, e.g., Scotch pine or Douglas fir, followed by spruce, is useful for soft, highly absorbent products. Deciduous trees, with the exception of the beech, generally produce a low absorbency.
Because of the scarcity and increase in cost of raw materials, greater efforts are made today to use waste paper and lower grade pulp. These raw materials, however, because of their high freeness, produce compact paper web with a low absorbency. Moreover, drainage on papermaking machines also deteriorates because of the high freeness, which also reduces the speed of the papermaking machines.
Types of tissues, such as, for example, tissues and kitchen paper towels, may have more or less wet strength. Cationic wet strength agents, such as, for example, polyamideamine-epichlorohydrin condensation products, are used to increase wet strength.
The creping of the paper is executed, for example, so that the paper web can be guided onto a can dryer with a large diameter and dried there and removed from the cylinder surface by means of a so-called crepe ductor at the end of the process in the cylinder. The extent of the creping is determined by the difference in the speed between the can dryer and the subsequent rolling up.
With use of high-quality fibers, it was necessary in part to improve the required adhesion between the paper web and the can dryer by so-called creping aids (adhesive agents). Increased use of waste paper with a high freeness, as well as a high proportion of filler and screened stock, as raw material for tissues generally leads to a deterioration in drainage in the wire part, greater adhesion to the can dryer, and considerable abrasion of the crepe ductor. The chemicals used to increase wet strength further reduce drainage and the absorbency of the paper and increase the adhesive effect on the can dryer.
Absorbent cellulose products, which are produced by dry defibration from cellulose pulp or cellulose fibrous pulp with floc formation, are used in sanitary products such as diapers and sanitary towels or napkins. In this case, the cellulose pulp should possess a low mechanical strength to facilitate the separation of fibers without their degradation and to reduce the energy required for the separation. Flocs obtained after the dry separation should possess a good fluid absorption capacity and a short absorption time.
The use of cationic surface-active agents such as quaternary ammonium compounds to reduce adhesion of cellulose fibers is known. These compounds have a considerable adverse effect on water absorption time. Additional disadvantages of the quaternary ammonium compounds are corrosion damage to equipment and frequently the reduction of the lightness of flocs, because the compounds typically have a chloride ion as the anion.
The reduction of adhesiveness by addition of nonionic substances to cellulose pulp is also known. According to German Offenlegungsschrift No. 19 55 454, nonionic substances, which are ethoxylated or propoxylated aliphatic alcohols or alkyl phenols, are used. Swedish Pat. No. 402,607, cited in Chemicals Abstracts Vol. 89, No. 181,429, shows a process in which alkoxylated aliphatic alcohols are used as retention agents in combination with quaternary ammonium salts.
An additional process is known from German Offenlegungsschrift No. 29 29 512, in which nonionic compounds are used in the preparation of absorbent cellulose pulp; in this case, these compounds consist of partial fatty acid esters of polyols with 2 to 8 carbon atoms or their anhydrides, i.e., anhydrous derivatives such as, for example, internal ethers, or consist of polyethylene or polypropylene glycols with molecular weights up to 500.